1. Field of the Invention
This invention relates to a deflection yoke, a deflection device, and a monochrome CRT display, and more particularly to a deflection yoke and a deflection device useful for single beam deflection in a large monochrome CRT display, or a high resolution FST scanner, etc., and a monochrome CRT display using such a deflection device.
2. Description of the Prior Art
In CRTs, since the beam arrival distance at the central portion of the screen and that at the peripheral portion thereof are different from each other, even if an adjustment is made at the central portion of the screen so that the most satisfactory focus is provided, the focus may become unsatisfactory at the periphery of the screen (deflection defocus). Further, a picture to be originally displayed as a rectangle may be displayed as a distorted one (deflection distortion).
For this reason, in monochrome CRT displays such as display monitors or television receivers, etc., using a conventional monochrome CRT, the winding distribution of a deflection coil is adjusted, or a correction magnet is arranged at a suitable position. Further, in order to improve the deflection defocus, a dynamic focus to modulate a focus voltage in a parabolic manner in correspondence with the scanning of beam is carried out.
On the other hand, in display monitors or television receivers using a color CRT, there is known a technology to vary the horizontal deflection magnetic field distribution in synchronism with the vertical deflection to thereby make a correction of convergence (Japanese Utility Model Application No. 139304/1984).
In recent years, it has been increasingly demanded that monochrome CRT displays have enlarged screens, increased deflection angles, flatness, and high resolution. To meet these demands, still improvements in the deflection defocus and the deflection distortion are necessary.
However, with the conventional technologies to adjust a winding distribution of a deflection coil, to provide a correction magnet, and to modulate a focus voltage, there is the problem that a sufficient improved effect cannot be provided under the condition of an enlarged screen more than 15 inches, an increased deflection angle more than 90 degrees, a high flatness factor more than curvature of 1 m, and a high resolution more than 1000 lines or 4 lines/mm.
On the other hand, as stated above, in the color CRT displays, there is known the conventional technology to vary the horizontal deflection magnetic field distribution in synchronism with the vertical deflection to make a correction of convergence. However, in the monochrome CRT display where the concept of convergence itself does not exist, application of such a conventional technology is not conceived at all as a matter of course.